Transcript TBM Safety Update - UCLA Dept. of Mechanical Engineering

Safety and Tritium R&D
B. J. Merrill and D. A. Petti
Fusion Safety Program
US TBM Meeting
INL, August 10-12, 2005
Presentation Outline
• Overview of safety analysis of the Dual Cooled Lead Lithium
(DCLL) test blanket module (TBM)
• Discuss safety issues that need to be resolved based on
present analysis results
• Look forward from where we stand now to what will have to
be accomplished both analytically and experimentally in order
to obtain operation approval for the DCLL TBM
• Estimate the resources that will be required to reach the final
goal and present a rough time schedule for the required work
• Summarize the key points to focus future safety activities
DCLL TBM Safety Analysis Overview
The safety analysis required by ITER for the DCLL TBM
Design Description Document (DDD) focused on four areas of
safety concern:
• Radioactive source terms that can be released during normal
operation or accident conditions
• Pressurization events that could fail ITER radioactive
confinement barriers (e.g., vacuum vessel (VV), confinement
building rooms, etc)
• TBM decay heat removal by thermal radiation to the basic
machine maintaining TBM FW temperatures < 350oC in the
post-shutdown period
• Hydrogen and heat generation from chemical reactions
between ITER cooling water and the PbLi and beryllium of the
TBM
DCLL Radioactive Source Terms
• Where do we stand? An estimate can be made based on present
ITER site boundary dose limit for TBMs of 0.5 mSv during an
accident, { assuming only a single nuclide is released, that the
release is stacked, and allowing for two possible weather conditions,
conservative weather (CW) and average weather (AW) }, as follows:
– Tritium release of between 14 g for CW or 70 g for AW compared to a
total TBM system tritium inventory of ~0.3 g
– Po-210 release of between 1.4 Ci for CW or 15 Ci for AW compared to
the TBM inventory of 1.8 Ci (possible problem area)
– Hg-203 release of between 1310 Ci for CW and 13,600 Ci for AW
compared to a TBM inventory of 36 Ci
– F82H oxide release at 700ºC of between 8 days for CW and 80 days for
AW compared to a building isolation time of 30 minutes
• The ITER in-facility annual release limit for TBMs will be ~100 mg-T;
however the predicted system permeation rate is ~470 mg-T/a for a
T2 pressures above the Pb-17Li of ~2 Pa (problem area)
Pressurization Events
• The required ITER safety assessment of the DCLL TBM DDD examined three
loss-of-cooling-accidents (LOCA), which are:
– Ex-vessel LOCA to assess TBM vault pressurization
– Coolant leak into TBM breeder or multiplier zone to assess module and tritium
extraction gas system pressurization
– In-vessel TBM coolant leak analysis to demonstrate a negligible pressurization of
ITER’s first confinement barrier (i.e., ITER VV)
0.20
.20
Pb-17Li - water reaction
.16
Test cell
TBM base case
Pressure (MPa)
Pressure (MPa)
• The safety function of
the ITER VV pressure
suppression system
was not compromised
and the vault design
pressure were not
exceeded, meeting
ITER TBM safety
requirements
0.15
ITER-FEAT multiple
tube in-vessel break
.14
.12
Vault
.10
VV
0.10
2800
2825
2850
2875
Time (s)
2900
VV pressure during and
in-vessel TBM LOCA
.08
2600
2800
3000
3200
Time (s)
Test cell, TCWS vault and VV pressures
during an ex-vessel TBM LOCA
Decay Heat Removal
• The ITER safety assessment
for the DCLL TBM DDD
demonstrated that the TBM
decay heat could be removed
by thermal radiation to the
ITER VV
• The TBM FW temperature
drops below 350ºC within
3 days, with the primary
reason for temperatures in
excess of the ITER FW
temperature during this time
period being the latent heat
capacity of the Pb-17Li and not
decay heating
Hydrogen Generation from Chemical Reactions
• The chemical reactions of concern for the TBM are beryllium
and Pb-17Li reacting with H2O
– ITER requires that the Pb-17Li volume be limited to
0.28 m3 to ensure that H2 production is less than 2.5 kg
– Alternatively, a detailed analysis of PbLi/H2O interaction
must be performed that considers a Pb-17Li spray into
water (spray droplets that are ~ 2 mm in radius); this
analysis is problematic because reaction rate data does
not exist for such droplets
Jeppson’s* experiment for
PbLi/H2O pouring contact mode is
(2 g of 600°C PbLi into 4000 g of
95°C H2O, which gives an initial
drop radius of ~8 mm)
– Our DDD relied on data from a single test (pouring
contact mode) that indicates that only ~50% of the Li will
react; however only the quantity of H2 generated and the
time to achieve this quantity of H2 were reported and
very little additional information given regarding
important modeling phenomena such as Pb-17Li
fragmentation, transient temperatures, and reaction rates
at various conditions.
• FW beryllium/H2O reaction will not produce more than 2.5 kg
even if all of the beryllium is reacted
*D. W. Jeppson, “Fusion reactor breeder
material safety compatibility studies,” Nuclear
Technology/Fusion, 4 (1983), p. 277-287.
Looking Forward
• Based on two presentation made at TBWG-15:
– Iseli’s (ITER-IT) presentation on TBM Safety described the ITER safety
approach and confinement strategy
– J.-Ph Girard (EDFA) presentation described the evolving approach for
Licensing of Experimental Devices for ITER, indicating that the safety
approach is still under development
• It appears that TBMs will have to be licensed, and at the present time
there is great deal of uncertainty regarding:
– Methods and guidelines for TBM safety analyses and documentation
 Will
the ITER radiological and hydrogen generation limits be acceptable or will new
limits be established?
 Will
additional accidents need to be analyzed, and on what basis will they be
selected?
 What
computer codes will be allowed for safety analysis and what level of quality
assurance and design qualification will be required?
Looking Forward (cont.)
Uncertainties:
– Licensing approach, three are being considered

Experiments considered and analyzed in initial safety files
This is presently the favored approach for ITER (Girard EDFA) but the worst
possible approach for a staged TBM approach because all of the planned TBMs
would have to be designed and qualified prior to ITER operating

Experiments with no extensive description
Approval as experiments mature but must stay within an initially defined safety
envelope – more favorable for a staged TBM philosophy

Non-scheduled experiments
New licensing process per TBM
– CEA requirements (not yet defined), however rough cost estimates for design related
safety work based on similar work done during the ITER EDA is:

Quality assurance, computer code V&V, historical control and design qualification
could become dominate safety concerns for design activity requiring 1 to 1.5 FTE/yr
effort for a safety analyst over the design life of the project for a full TBM approach
and ~0.5 FTE/yr for a partial TBM or sub-module in EU TBM
Looking Forward (cont.)
• If ITER analysis rules can be used as a guide, then we have identified several
areas of required safety R&D
– Additional Pb-17Li/H2O reactions test are required to support our contention that only 50%
of the Li reacts when a hot atomized spray of Pb-17Li contacts relatively cool water
– Tritium permeation through cooling system pipe walls (Pb-17Li and He) will require
permeation barriers. Alumina coatings on steel (50 μm) have been demonstrated to
reduce permeation by 10 to 1000, but it is not clear that these coatings will survive the
temperature swings of the helium piping during pulsed operation. These coating will be
engineered administrative controls for personnel safety.
– The quantity of Po-210 produced approaches levels of a safety concern if we are asked to
assume a complete release of this inventory directly to the atmosphere as a ground
release. Cleanup of the Po-210 may be required; however if extraction columns are used
to remove T2 from the Pb-17Li then most of the Po-210 will likely end up in the tritium
purge gas system
– Present estimates of TBM tritium inventories are based on a prototype ferritic steel tube
vacuum permeator keeping the tritium partial pressure to less than 2 Pa. Test will have to
be conduct to prove this technology. If extraction columns are used, then the tritium
inventory could grow to 7 g, requiring more detailed accident mobilization and release
calculations to demonstrate that the TBM meets radiological limits
Safety R&D
• The anticipated Safety R&D projects required to resolve these
issues are:
 PbLi spray/H2O reaction testing to determine percent of Li
reacted for prototypical conditions. ($2 - 5 M - 3 to 5 years)
 Tritium permeation barrier integrity during thermal cycling
($2 - 4 M; 3 to 5 years)
 Tritium extraction tests to verify vacuum permeators ($2 - 4
M; 3 to 5 years)
 Costs and schedules will be refined in more detail as we go
forward and optimize conceptual approaches to each
experiment
• Cost estimates are based on similar work done by the FSP
during the ITER EDA.
Potential Safety Experiments
Supporting the US ITBM Program
PbLi Reactivity During LOVA
• simulates LOVA with pooling
water and sprayed molten PbLi
• single and multiple droplet sizes
or streamed injection
• variable surface area of exposed
water
• gas analyzer measures moisture
content and H2 generation
• view ports allow imaging of
reaction surfaces, temperature
measurements, and droplet
dynamics
Potential Safety Experiments
Supporting the US ITBM Program, cont.
Thermal Cycle Performance of He Pipe Permeation Barriers
• simulates thermal stress
degradation of permeation barrier
coatings for He pipes
• configuration matched to TBM
design for coated components
• utilize tritium for barrier
technology qualification
• external thermal cycles followed
by testing in permeation rig for
integrated effects
• in-situ thermal cycling in
permeation rig for barrier dynamic
response
Summary